In a semiconductor device manufacturing process, a liquid process is performed on a target substrate such as a semiconductor wafer (hereinafter, referred to as a “wafer”). As an example of such a liquid process, there is a cleaning process of the wafer by a cleaning solution. A liquid processing unit for used in the liquid process includes, for example, a cup configured to receive a processing solution; a rotation holding unit such as a spin chuck provided in the cup; and a processing solution supply nozzle configured to supply the processing solution to the substrate. In the cleaning process of the wafer, by supplying multiple kinds of processing solutions in a preset sequence to a front surface of the wafer being rotated, the liquid process is performed.
The spin chuck and the cup for used in the liquid process are provided in a common housing so as to be separated from an outside atmosphere. Clean air is supplied from a fan filter unit (FFU) provided on the housing, and a downward flow of the clean air is formed within the housing. The downward flow of the clean air suppresses generation of particles and mist caused by loading/unloading the wafer or performing the liquid process. As a result, the wafer and the inside of the housing are maintained in a clean state.
In the cleaning process, an alkaline or acid processing solution is supplied to the wafer, and the wafer is cleaned by a rinse solution such as deionized water (DIW). Thereafter, by supplying IPA (IsoPropyl alcohol) to the wafer, an IPA drying process is performed, and the processing solution remaining on the front surface of the wafer is removed with the IPA. During the IPA drying process, an atmosphere around the wafer needs to be maintained at low humidity.
In the liquid process for performing on the front surface of the wafer having thereon a metallic wiring such as a copper wiring, in order to prevent oxidation of the metallic wiring, it is required to control oxygen concentration on the front surface of the wafer to be low.
In this regard, for example, Patent Document 1 describes a technology capable of preventing a watermark caused by particles entering a rinse solution and a native oxide film by forming a downward flow of an inert gas within the entire apparatus so as to cover an entire target surface of a substrate. However, in Patent Document 1, since the inert gas is supplied into the entire space of the apparatus, running costs for the liquid process are increased.
Meanwhile, Patent Document 2 describes a liquid processing apparatus that performs an etching process by supplying a processing solution to a bottom surface and a side surface of a target substrate. In the liquid processing apparatus, in order to prevent the processing solution from entering the top surface of the target substrate, a top plate is provided so as to cover a top surface of the target substrate, and an inert gas is supplied from a central portion of the top plate toward the top surface of the target substrate. In the liquid processing apparatus, a liquid process is performed on the bottom surface and the side surface of the target substrate. However, when the liquid process is performed on the entire top surface of the target substrate, in order to avoid interference between a processing solution supply nozzle and the top plate, a special processing solution supply unit is required. Further, when the target substrate is transferred, in order to avoid interference between the target substrate and the top plate, a moving device for relatively moving the top plate with respect to a holding unit for holding thereon the target substrate is additionally required.    Patent Document 1: Japanese Laid-Open Patent Application No. 2003-174006: Claim 1 and FIG. 1    Patent Document 2: Japanese Laid-Open Patent Application No. 2010-028059: Claim 4, paragraph 0021, and FIG. 1